In patent application No. PCT/AU83/00003 there is described a mechanism for varying the valve timing an duration of lift of the valves of the internal combustion engine, the engine having a cam shaft and hydraulic cam followers, characterized in that the bleed of hydraulic oil from the hydraulic cam follower is controlled through a secondary cam follower, the secondary cam follower operating in a housing adjustably rotatable about a secondary cam shaft. In an embodiment described in that specification the secondary cam shaft actuates the secondary cam follower through an intermediate lever which is pivoted to the housing about the secondary cam follower, this lever then being shaped to give a reduced lift to the secondary cam follower by virtue of the secondary cam follower being in contact with the lever between its pivot point and the point at which the cam operates.